1. Field of the Invention
The present invention relates to an image processing apparatus and method thereof, and an image capture apparatus, which generate an image having a broad dynamic range by composing a plurality of captured images having different exposure amounts.
2. Description of the Related Art
In general, an image processing apparatus which composes a plurality of captured images having different exposure amounts to broaden a dynamic range, and executes tone compression to fit the dynamic range of an output apparatus has been proposed (Japanese Patent Laid-Open No. 07-131704 (to be referred to as literature 1 hereinafter)). Also, image processing which converts an input image into images of a plurality of resolutions, and optimizes tone compression characteristics for each small region around a pixel of interest of the input image using these images so as to compress the dynamic range of the input image has been proposed (Japanese Patent No. 03731577 (to be referred to as literature 2 hereinafter)).
However, with the technique described in literature 1, an image of a broad dynamic range, which is generated by composing a plurality of images having different exposure amounts, undergoes tone compression to fall within the dynamic range of an output apparatus to have uniform characteristics according to a brightness in a frame as shown in FIG. 16. For this reason, a brightness region where tone reproducibility is lost is generated.
On the other hand, with the technique described in literature 2, in order to generate tone compression characteristics, multi-resolution processing is required. That is, images of a plurality of types of resolutions, which are generated from an input image, have to be referred to at the same timing. For this purpose, a timing has to be adjusted by buffering a high-resolution image in a frame memory while generating a low-resolution image. Buffering of an image using the frame memory imposes a heavy load on an image capture system especially when a moving image is to be captured and when an image size and bit width are large.